This research project deals with problems of mammalian developmental genetics. In particular it is concerned with the identification of specific genes, both structural and regulatory, which control various aspects of embryonic development and cell differentiation on levels of morphogenesis and biochemistry. Mutations in the mouse affecting development and differentiation serve as tools in these studies. The identification of genetically caused specific developmental defects provides the potential of elucidating the corresponding normal mechanisms of development and their genetic control. Particular attention centers on complex genes, e.g. the T-locus and several lethal albino deletions in the mouse. The latter appear to include a series of regulatory genes concerned specifically with the control of liver cell differentiation. Methods of genetics, developmental biology, biochemistry, somatic cell genetics, electronmicroscopy, cytology and molecular biology serve these studies. The research proposed here provides model systems for the study of birth defects and inborn errors of metabolism in humans. It opens up new views on the etiology of congenital malformations and underscores the genetic heterogeneity of conditions with similar appearances, e.g. glycogen storage diseases.